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Divestitures, Assets Held for Sale, and Acquisitions Divestitures and Assets Held for Sale (Details) $ in Thousands |  |  | 3 Months Ended | 12 Months Ended
--- | --- | --- | --- | ---
Mar. 26, 2018 USD ($) a | Mar. 10, 2017 USD ($) | Mar. 31, 2018 USD ($) | Mar. 31, 2017 USD ($) | Dec. 31, 2017 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |
Net divestiture proceeds |  |  | $ 490,780 |  | $ 744,333 |
Net gain on divestiture activity |  |  | 385,369 |  | 37,463 |
Disposal Group, Including Discontinued Operation, Property, Plant and Equipment, Noncurrent |  |  | 234,618 |  |  | $ 111,700
Asset retirement obligations associated with oil and gas properties held for sale |  |  | 23,139 |  |  | 11,369
Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member] | PRB Divestiture 2018 [Member] |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |
Net Acreage Divested | a | 112,000 |  |  |  |  |
Net divestiture proceeds | $ 490,800 |  |  |  |  |
Net gain on divestiture activity |  |  | 409,200 |  |  |
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |
Asset retirement obligations associated with oil and gas properties held for sale |  |  | 23,100 |  |  |
Assets held for sale, Loss (Gain) on Write-down |  |  | 24,100 |  | 359,600 |
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Divide County Divestiture and Halff East Divestiture 2018 [Member] |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |
Disposal Group, Including Discontinued Operation, Property, Plant and Equipment, Noncurrent |  |  | 234,600 |  |  |
Gross Divestiture Purchase Price |  |  | 292,300 |  |  |
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Divide County Divestiture 2018 [Member] |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |
Income (Loss) from Individually Significant Component Disposed of or Held-for-sale, Excluding Discontinued Operations, Attributable to Parent, before Income Tax |  |  | $ (11,497) | [1] | (332,719) |
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Divide County Disposal Group [Member] |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |
Assets held for sale, Loss (Gain) on Write-down |  |  |  |  | 359,600 |
Net Divestiture Proceeds Received at Closing [Member] | Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member] | Non-Operated Eagle Ford Divestiture 2017 [Member] |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |
Net divestiture proceeds |  | $ 747,400 |  |  |  |
Net Divestiture Proceeds After Final Purchase Price Adjustments [Member] | Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member] | Non-Operated Eagle Ford Divestiture 2017 [Member] |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |
Net divestiture proceeds |  |  |  |  |  | 744,100
Estimated Net Gain [Member] | Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member] | Non-Operated Eagle Ford Divestiture 2017 [Member] |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |
Net gain on divestiture activity |  |  |  |  | $ 398,100 |
Final Net Gain [Member] | Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member] | Non-Operated Eagle Ford Divestiture 2017 [Member] |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |
Net gain on divestiture activity |  |  |  |  |  | $ 396,800
[1] | (1) Loss before income taxes reflects oil, gas, and NGL production revenue, less oil, gas, and NGL production expense, depletion, depreciation, amortization, and asset retirement obligation liability accretion expense, and impairment expense.

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- Definition Noncurrent portion of the carrying amount of a liability for an asset retirement obligation for an asset held for sale. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees. + References No definition available. + Details
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- Definition Amount classified as property, plant and equipment attributable to disposal group held for sale or disposed of, expected to be disposed of after one year or the normal operating cycle, if longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=84176398&loc=d3e2941-110230 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=65878427&loc=SL51721533-107759 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=68055307&loc=d3e2510-110228 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 45 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=65878427&loc=d3e1107-107759 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 50 -Paragraph 5B -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=64827811&loc=SL51721673-107760 + Details
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